The Bright Extragalactic ALMA Redshift Survey (BEARS) I: redshifts of bright gravitationally-lensed galaxies from the Herschel ATLAS

TL;DR

This paper reports spectroscopic redshift measurements for 71 bright, high-redshift, gravitationally-lensed galaxies from the Herschel H-ATLAS survey, demonstrating ALMA's efficiency as a redshift hunter and analyzing lensing effects.

Contribution

It introduces an optimized ALMA tuning method for redshift determination and provides a large, robust dataset of high-redshift galaxy redshifts and lensing magnification estimates.

Findings

Redshifts range from 1.41 to 4.53 with a mean of 2.75.

CO emission line widths vary from 110 km/s to 1290 km/s.

Lensing magnification factors are consistent with galaxy-galaxy lensing models.

Abstract

We present spectroscopic measurements for 71 galaxies associated with 62 of the brightest high-redshift submillimeter sources from the Southern fields of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), while targeting 85 sources which resolved into 142. We have obtained robust redshift measurements for all sources using the 12-m Array and an efficient tuning of ALMA to optimise its use as a redshift hunter, with 73 per cent of the sources having a robust redshift identification. Nine of these redshift identifications also rely on observations from the Atacama Compact Array. The spectroscopic redshifts span a range $1.41<z<4.53$ with a mean value of 2.75, and the CO emission line full-width at half-maxima range between $\rm 110\,km\,s^{-1} < FWHM < 1290\,km\,s^{-1}$ with a mean value of $\sim$ 500kms$^{-1}$, in line with other high-$z$ samples. The derived CO(1-0) luminosity is significantly elevated relative to line-width to CO(1-0) luminosity scaling relation, which is suggestive of lensing magnification across our sources. In fact, the distribution of magnification factors inferred from the CO equivalent widths is consistent with expectations from galaxy-galaxy lensing models, though there is a hint of an excess at large magnifications that may be attributable to the additional lensing optical depth from galaxy groups or clusters.